1. Field of the Invention
The present invention relates to a target containing a refractory metal element and a chalcogen element and to a method for producing the same. The invention also relates to a memory including a memory device having an ionization layer formed using a target and to a method for producing the same.
2. Description of the Related Art
A high-speed, high-density DRAM has been widely used as a random access memory in an information-processing apparatus, such as a computer.
However, DRAMs are volatile memories that lose their contents when the power is turned off, and the written information (data) has to be frequently refreshed, i.e., the data needs to be frequently read, reamplified, and rewritten.
As non-volatile memories that do not lose their contents when the power is turned off, a flash memory, an FeRAM (ferroelectric random-access memory), an MRAM (magnetic memory device), and the like have been proposed, for example.
These memories are capable of maintaining the written information for a long period of time without power supply.
Further, because these memories are non-volatile, they do not require refreshment, and the power consumption can be reduced accordingly.
Therefore, various non-volatile memories as those mentioned above have been widely studied and commercially developed.
However, such non-volatile memories have both merits and demerits.
Flash memories have high integration density, but are disadvantageous in terms of operation speed.
FeRAMs pose a limitation on the microprocessing for high integration, and also have problems in the production process.
MRAMs have problems in terms of power consumption.
Accordingly, a new type of memory device has been proposed, which is particularly advantageous to overcome the limitation on the microprocessing of a memory device.
This memory device has a structure in which an ion conductor containing a specific metal is sandwiched between two electrodes. When a voltage is applied between the two electrodes, the metal in each electrode diffuses as ions into the ion conductor, thereby changing the resistance, capacitance, or like electrical characteristics of the ion conductor.
A memory device can be configured to utilize such characteristics.
Specifically, the ion conductor includes a solid solution of chalcogen elements (S, Se, Te) and a metal. More specifically, the ion conductor includes a material having Ag, Cu, and Zn dissolved in AsS, GeS, and GeSe (see, e.g., JP-T-2002-536840 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)).
It has also been proposed that a layer of such an ion conductor (hereinafter referred to as an ionization layer) contains, in addition to the chalcogen elements, Zr, Al, and like elements (see, e.g., JP-A-2009-43758).